1. Field of the Invention
The present invention relates to a disk drive which highly accurately positions a recording/reproducing head on a target track of a disk serving as a recording medium by an actuator. More specifically, the present invention relates to a technique for suppressing deviation of a head from a target track by a disturbance that acts on an actuator.
The present invention also relates to a disk drive having a load/unload mechanism which unloads a head to a head rest member such as a ramp block outside of a disk when the head is stopped and which loads the head onto a disk surface from the head rest member when the head is used, and to a technique for stably loading the head onto the disk surface under appropriate velocity control even if a disturbance on the head rest member is great.
2. Description of the Related Art
In recent years, disk drives such as magnetic disk drives are increasingly made small in size and large in capacity and tracks increasingly tend to be high in density and narrow in pitch, accordingly. Therefore, it has become important to position a head on a target track with high accuracy. Namely, the head reads servo information recorded on the disk in advance to generate a position error signal for the head relative to the target track and the positioning of the head is controlled so that the position error signal can be minimized. To accelerate a positioning velocity, the control frequency of a positioning control system is set high. However, the inherent mechanical resonance of an actuator of the head makes the positioning control system instable. Under these circumstances, there is naturally a limit to setting the control frequency high.
As the track is higher in density and narrower in pitch and the actuator is made smaller in size and lighter in weight, the influence of a disturbance that acts on the actuator on the positioning control system increases. On the other hand, the highly accurate positioning of the head is strictly required. To meet the demand, it is significant to reduce the disturbance which causes deterioration of the head positioning accuracy. To this end, a technique for estimating a disturbance based on a head position signal obtained from servo information recorded on the disk and a driving signal for the actuator, and for compensating for the disturbance by feed-forward control has been conventionally proposed.
However, the servo information on the disk is discrete information having a constant sampling cycle and the head position signal that reproduces the servo information is not a continuous signal. Because of the restriction of the sampling frequency of the servo information, a control band of the disturbance estimation means has an upper limit and the presence of the upper limit makes it disadvantageously difficult to accurately estimate the disturbance. As a result, it is disadvantageously difficult to make the head always accurately follow up the target track.
Furthermore, the disturbance changes greatly on the head rest member due to sliding friction, so that a velocity of a head slider changes considerably. Even if the head slider velocity is feedback-controlled, the change of a head loading velocity is great and the head slider is often disadvantageously struck against the disk.